In the art of stringed musical instruments particularly electric guitars and basses, the mass, density, and structural rigidity of the bridge structure, including the bridge saddles across which the strings pass at one or more speaking end thereof, has an enormous effect on the vibrating characteristics of the strings of the instrument. Specifically the lateral and vertical rigidity of the bridge saddles and the mass of the support structure determine how much of the string's kinetic energy will be absorbed by the instrument structure during the period after which the string has been exited into vibration. The more solid and massive the structure, the less the energy loss in the string. Among musicians, generally speaking, the longer the string vibrates after being plucked, i.e. the longer the "sustain" of the instrument, the better. Therefore dense, rigid bridge structures are popular.
In musical instruments, another important consideration apart from the "sustain" is the ability of the instrument to stay in tune. If excessive friction, in the longitudinal direction, is encountered at some point between the anchored ends of the strings of the instrument, during playing and/or tuning of the instrument, inequities in the tension in the string at either side of the point of the friction occur.
In practice this means that if, for example, the speaking portion of a string is manually stretched or "bent", during playing, enough that the point of the string that engages a high friction point on a bridge saddle is drawn across the saddle toward the speaking portion of the string, when the manual bending tension is released, due to the friction of the bridge saddle, the point of the string that engages the bridge saddle may not be the same as the point of the string that engaged the bridge saddle before bending. The result will then be that the tension and therefore the tuning of the speaking portion of the string will not be the same.
The tuning characteristics of instruments having the above problem are exasperatingly unstable.
In order to stabilize the tuning characteristics of stringed instruments, bridges and nuts encorporating rollers intended to eliminate longitudinal friction in the string path are well known. However in these systems the problem of lateral play exists in the bearings of the rollers. This lateral play tends to absorb the kinetic energy of the string and thus kill the sustain of the string. The lateral play in the rollers also tends to result in unpleasant noises and rattling as well as adding unpleasant harmonics to the string vibrations.
In pin bearings, this lateral play can sometimes be eliminated by tightening the seating of the bearing however this results in friction in the roller which negates the friction reducing effect the roller was initially intended to provide.